Is this when you are running a total station with Access 2017 as a setup ? I have experienced something similar, Trimble suppport came back with the following reply.

"this has to do with the auto connect function in the access software 2017.00 setup, for the Focus30/35 unit, if you switch this off in the auto connections setup in Access this should solve the issue," its suggested that you switch off any instrument in those settings that you are not using, which includes the 5600 etc, I keep the GNSS setting and the S series total station settings on have found the error did not occur as often as it did previously. I have been informed that this bug would be fixed in the next version of Access 2017, I have downgrade the Access firmware to Access 2016.12, which seems to work, and that version does not have the Focus30/35 option available in the Auto connect menu.